Abstract Our novel in vivo murine data uncovered a constitutive, extracellular vesicle-based feedback loop between circulating RBCs and bone marrow precursors. Based on our results, the overall hypothesis of this application is that bioengineered, host RBCs, loaded with custom genome editing machinery may represent an effective approach to target and correct various molecular defects responsible for severe hemoglobinopathies and thrombocytopathies. Our results also show that cells in either acute hypoxic environments such as ischemic tissues, or chronic hypoxic settings such as cancers, also become targets for the RBC-EVs, expanding the usefulness of our proposed delivery platform. Circulating RBCs are distinct among all body cells, having a cytoplasm devoid of organelles, endo/exocytic pathways, DNA, or protein synthesis. Hence, we believe that the RBC cytosol is an ideal carrier for the gene editing machinery components as: i) the cargo is shielded from the immune surveillance of the host, ii) the intended target(s) of the cargo are likely not be present in circulating RBCs, therefore unlikely to impact the cell functions, and (iii) RBCs generate extracellular vesicles that upon fusion with target membranes transfer the EV content into the cytosol, avoiding the lysosomal compartment. Our long term aim is to perfect our ex vivo liposome-based cell loading technology to enable us to load a patient?s own RBCs with the ?condition-tailored? combination of gene editing machinery, and transfuse them back into the donor to target and correct the genetic condition. During the course of this project we will: i) develop a high throughput RBC-loading method that will deliver biologicals into RBCs with minimal effect on RBC mechanical and antigenic properties, and ii) test, in vitro the effectiveness of the bioengineered RBCs to deliver via RBC-derived EVs a functional gene editing machinery target cells, and then validate in vivo the efficacy of GEM delivery using a murine model first, and then a large animal model (pig).